The present invention relates to a osteosynthesis surgical pin for an osteosynthesis plate or for the coaptation of bone fragments, this pin being adapted to be driven by a driving motor used as ancillary means.
Due to the difficulties involved in the manual fitting of surgical screws in satisfying operating conditions, especially when the screws have very small sizes, attempts have been made to improve the fitting time as well as the efficiency and safety of the surgeon operating procedure.
In order to reach this object, a first solution has been proposed by French patent 87 18 540 (2 625 430) GUINOUNET which involves cutting out in one piece a screw, one end portion of which is sharp and provided with a tapping notch. The other end portion is equipped with a handling rod or shank adapted to be inserted into the chuck of a driving rotating motor and firmly maintained within the latter. The separation of the handling shank is carried out after the screw has been fitted. The shank is connected to the remaining portion of the threaded rod by a restriction of less resistance to a given torque. The surgeon can thus screw directly and quickly with the screwing tool, which makes it possible to reduce the operating time.
However although interesting, this kind of pin could not in fact satisfy the surgeons, since it very imperfectly achieved its intended result, so that it was quickly abandoned by its inventor.
In order to ensure very safely the fitting of a small size surgical screw i.e., having a diameter of substantially 2 mm and a length of substantially 12 mm, by means of a ancillary driving device and for fitting the screw in good operating conditions, particularly for very delicate osteosynthesis, such as foot bone osteosynthesis, the introduction of the screw must be absolutely correctly effected, while permitting the surgeon to very closely control its revolution. While this method may work effectively when the screwing is manual, the results are different when screwing is submitted to the rotation speed of a motor i.e. to a speed of substantially 100 to 200 r/minute.
The reason is the following: if the motor rotates at 100 r/minute and if the thread of the screw is 1 mm (frequently used for small screws), the surgeon has (for a screw having a 1 2 mm length) only 12/100minute until the screw head comes into contact with the bone, i.e. about 7 seconds. At 200 r/minute, the surgeon can have about 3 seconds. Beyond 200 r/minute, the surgeon must be very quick to give, if necessary, a translation movement to the motor, in order to cease the support.
In such case, the penetration of the cortical bone and the spongious bone must be suitably done, taking into account the rotation speed and the average mechanical resistance for the different bone walls.
For this reason, the end portion of the screw is designed in order to allow some control of the tapping, which can be carried out only relatively slowly and progressively, by reducing the bone portion in fine particles.
Besides, the screw disclosed in above FR-A-patent GUINOUNET 2 625 430 has miscellaneous drawbacks. The hexagonal head of the screw protrudes from the osteosynthesis plate, which may constitute an obstruction. Furthermore, for fixing osteosynthesis plates, screws having a milled head with a hexagonal recessed indentation are usually used. But due to the fact that the head is integral with the holding shank, it is not possible to provide the head with a hollow indentation. It is also necessary to be able to maneuver the screw manually, so as to complete the screwing or to unscrew it in order to remove it at the end of certain period of time.
Furthermore, with the use of this type of screw, the drilling is effected by means of the point of the screw and of a lateral notch which is provided not far from that point. This type of notch which serves essentially for tapping, does not permit drilling so that the penetration of the screw is effected forcefully more by percussion than by chip removal, at the risk of poor tapping and, therefore, of only an approximate fixation of the screw in its support.
Another important defect of the GUINOUNET screw consists in the fact that the sharp end portion of this screw can seriously damage the bone. Indeed, in this prior screw, the threads begin on the sharp end portion. Consequently, in comparatively thick cortical bones (2 mm), the advance speed of the screw will be directly transmitted to the thread of the screw. If at that time, the cortical portion of the bone is not already pierced, the screw will fracture the bone due to a too high penetration speed into the bone, which obviously constitutes a serious drawback.
Lastly, this prior screw does not permit a piercing sufficiently symmetrical in rotation conditions supported by the screw, due to the lateral notch of its head portion.
The VAN OMMEREN U.S. Pat. No. 610,423 discloses a screw adapted to be used in wood, and not for surgical uses. This screw has a head provided with lateral notches permitting its handling by a screw driver, these opposite notches preventing the screw driver from slipping therefrom. This screw does not relate to surgical uses and is not even adapted to be driven by a motor.
It must be added that providing longitudinal notches within the smooth rod portion close to the head makes the screw brittle. Besides, when screwing, a part of these longitudinal notches is embedded in wood, which slows down the screwing, and makes necessary a higher screwing torque, since wood particles fill the empty notches. Consequently, such a screw is totally inadapted to surgical uses, especially in delicate small bones like foot bones.
The MYERS U.S. Pat. No. 3,208,328 relates to a kind of rivet for connecting to sheets of wood or metal (FIGS. 9-10). The head of this screw or rivet is not provided with diametrically opposite notches but is flat. In use, the screw is first inserted into a hole formed in the upper sheet, and then pierces the second sheet by means of its sharp end portion. The screw is handled by means of a tool 31 acting on a flat part 9.
Thus the screw is driven, not by its head, but through its flat portion. However, the end portion can be rounded (FIG. 3) when it is not necessary to make a passage hole in the upper sheet. The point 5 is necessary only for passing through sheet 30 to be connected to sheet 29, while the screw is already guided in the bore of the upper sheet 29.
Such kind of screw is completely inadapted for surgical uses and, in particular, the delicate treatment of small bones such as foot bones.
The MOORE U.S. Pat. No. 3,343,443 teaches a screw for wood or metal which can be inserted by means of a very powerful motor unit. This rivet assembly comprises a threaded rod with a self drilling end, and a shank divisibly attached to the head by a zone of reduced resistance to torque.
However MOORE does not teach the head of a pin having a pair of diametrically opposed notches permitting the head to be grasped by a corresponding tool, and the drill tip is not integral with the body of the pin so that this pin is not adapted for surgical uses and especially to the delicate field of foot bone surgery.